Android jetpack room 数据库的升级

如果用户设备上数据库版本为1

而当前要安装的App数据库版本为3怎么办

Room会先判断当前有没有直接从1到3的的升级方案，如果有，就直接执行从1到3的升级方案，如果没有，那么Room会按照顺序先后执行 Migration(1,2)、Migration(2,3)以完成升级。

修改dataBase文件

package com.anguomob.jecpack.database
 
import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import androidx.room.migration.Migration
import androidx.sqlite.db.SupportSQLiteDatabase
import com.anguomob.jecpack.bean.Student
import com.anguomob.jecpack.dao.StudentDao
import okhttp3.internal.Internal.instance
 
@Database(entities = [Student::class], version = 3, exportSchema = false)
abstract class MyDataBase : RoomDatabase() {
    companion object {
        var DATABASE_NAME = "my_db.db"
        private lateinit var instance: MyDataBase
 
        //数据库从1 到2 版本的升级
        var MIGATION_1_2: Migration = object : Migration(1, 2) {
            override fun migrate(database: SupportSQLiteDatabase) {
                //新增性别
                database.execSQL("ALTER TABLE student ADD COLUMN sex INTEGER NOT NULL DEFAULT 1")
            }
        }
 
        var MIGATION_2_3: Migration = object : Migration(2, 3) {
            override fun migrate(database: SupportSQLiteDatabase) {
                //新增性别
                database.execSQL("ALTER TABLE student ADD COLUMN `bar_data` INTEGER NOT NULL DEFAULT 1")
            }
        }
 
 
        fun getSingle(context: Context): MyDataBase {
            if (::instance.isInitialized.not()) {
                instance = Room.databaseBuilder(
                    context.applicationContext,
                    MyDataBase::class.java,
                    DATABASE_NAME
                )
//                    .allowMainThreadQueries()//允许主线程操作数据库
                    .addMigrations(MIGATION_1_2, MIGATION_2_3)
                    .build();
            }
 
            return instance;
        }
 
 
    }
 
 
    abstract fun getStudentDao(): StudentDao
 
 
}

 

 数据库的版本也修改一下。

其中呢数据bean也要跟着变化

package com.anguomob.jecpack.bean
 
import androidx.room.ColumnInfo
import androidx.room.Entity
import androidx.room.Ignore
import androidx.room.PrimaryKey
 
@Entity(tableName = "student")
data class Student(
    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "id", typeAffinity = ColumnInfo.INTEGER)
    var id: Int,
    @ColumnInfo(name = "name", typeAffinity = ColumnInfo.TEXT)
    var name: String,
    @ColumnInfo(name = "age", typeAffinity = ColumnInfo.INTEGER)
    var age: Int,
    @ColumnInfo(name = "sex", typeAffinity = ColumnInfo.INTEGER)
    var sex: Int,
    @ColumnInfo(name = "bar_data", typeAffinity = ColumnInfo.INTEGER)
    var bar_data: Int
) {
 
    @Ignore
    constructor(name: String, age: Int) : this(0, name, age, 1,1)
 
 
    @Ignore
    constructor(id: Int) : this(id, "", 0, 1,1)
}
 
 

弄完后可以导出来数据库

 在data/data/包名/database路径下的三个都导出到桌面一个位置

X:\Users\Administrator\Desktop

 然后用其他的数据库软件打开

看数据库就存在了sex 与bar_data字段